1. Field
The presently disclosed subject matter relates to a reflective real specular image forming element forming a real image (real specular image) of an observed object in a space of a viewer side and, a display device using the same and an optical device using the same.
2. Description of the Related Art
There have been suggested a display device for allowing a viewer to see a real image (real specular image) of an observed object in air by using the reflective real specular image forming element (see Reference 1 below).
Specifically, such a display device using the reflective real specular image forming element comprises a reflective real specular image forming optics being in a space of a viewer side; and an observed object disposed in a space opposite to the viewer side with respect to the reflective real specular image forming optics, where the reflective real specular image forming optics performs the formation of a real image (real specular image) of the observed object at a symmetrical position with respect to a plane of symmetry thereof.
The document Reference 1 explains unit optical elements (each so-called as a dihedral corner reflector) as the reflective real specular image forming optics wherein each of unit optical elements has two orthogonal minor surfaces (reflection surfaces) which are perpendicular to each other. The document Reference 1 discloses a reflective real specular image forming element (so-called a dihedral corner reflector array optical element) in which a plurality of dihedral corner reflectors are arranged regularly on one plane of an element face. The dihedral corner reflector array optical element specifically utilizes respective inner walls of square shaped holes made in a substrate while penetrating the element face as dihedral corner reflectors laid out in a grid pattern. Also, the dihedral corner reflector array optical element utilizes a plurality of transparent cube shape tubular bodies each perpendicularly protruding from the surface of the substrate made of a transparent material wherein inner wall surfaces of each transparent tubular body or prism body are used for the dihedral corner reflector.
In a plurality of the arranged dihedral corner reflector of the dihedral corner reflector array optical element, since each minor surface is disposed perpendicularly to the element face, light (emitted from the observed object existing on the one side of the element face) is reflected twice by the dihedral corner reflector during passing therethrough, and then by all light passed through the element, a real image is formed in a space of observed object absent on the other side of the element face. Namely, the dihedral corner reflector array optical element performs the formation of a real image in such a manner that the real image of the object exists symmetrical to the observed object with respect to the element face (the so-called plane of symmetry) of the dihedral corner reflector array optical element.
Reference 1: WO 2007-116639
There are various differences in the condition of observation in order to obtain the brightest floating image observed by using the dihedral corner reflector array optical elements having square shaped holes and alternatively having the cube prism bodies made of a transparent material such as acrylic resin because the transparent material differs in refractive index from the air.
In the conventional art, there is a characteristic and/or problem that it is hard to form a floating image with brightness sufficient to be distinguishable from background brightness if prism bodies having a low height are formed on the dihedral corner reflector array optical element.